Search Result for "dark matter":
Wordnet 3.0

NOUN (1)

1. (cosmology) a hypothetical form of matter that is believed to make up 90 percent of the universe; it is invisible (does not absorb or emit light) and does not collide with atomic particles but exerts gravitational force; 



WordNet (r) 3.0 (2006):

dark matter
    n 1: (cosmology) a hypothetical form of matter that is believed
         to make up 90 percent of the universe; it is invisible
         (does not absorb or emit light) and does not collide with
         atomic particles but exerts gravitational force